1. Field of the Invention
The present invention relates to an organic electroluminescent display device and a method of fabricating the same and, more particularly, to an organic electroluminescent display device having an optimum resonance structure.
2. Description of the Related Art
An organic electroluminescent display (“OLED”) device having a thin film transistor (“TFT”) is a self light-emissive type display device, which is attracting public attention as a next generation display device because of its wide viewing angle, excellent contrast ratio, and fast response speed.
The OLED device is classified as either an inorganic electroluminescent (EL) device or an organic EL device depending on the material used to form a light emitting layer. Compared to the inorganic EL device, the organic EL device may provide improved display performance in such characteristics as luminance, driving voltage, response speed, and can also provide a full-color display.
The OLED device has a full color feature because it may include a pixel comprising pixel regions defined by the intersection of a plurality of scan lines and a plurality of data lines, which can be arranged substantially perpendicular to each other. Each pixel region corresponds to either red, green, or blue colors.
Referring to FIG. 1, a typical full-color OLED device has a substrate 10 having a red pixel region (R), a green pixel region (G) and a blue pixel region (B); and a plurality of first electrodes 12 formed on portions of substrate 10 overlapping the red pixel region, the green pixel region and the blue pixel region. In the case of a top-emission type OLED device, the first electrode 12 can be a metal electrode, which may be either a reflecting electrode or a transparent electrode containing a reflecting layer.
In order to insulate the pixel regions and to define the pixel, an insulating material layer is deposited and patterned to form a pixel defining layer 14.
A hole injecting layer 16 and a hole transporting layer 18 are formed over the whole surface of substrate 10 to cover the first electrodes 12 as a common layer.
A light emitting material layer is deposited on portions of hole transporting layer 18 that overlap the respective pixel regions to thereby form red (R), green (G) and blue (B) light emitting layers 20.
If needed, a hole blocking layer 21, an electron transporting layer 22, and an electron injecting layer 23 are sequentially formed over the whole surface of substrate 10, and a second electrode layer 24 is formed on electron injecting layer 23. In a typical OLED, hole injecting layer 16, hole transporting layer 18, light emitting layer 20, hole blocking layer 21, electron transporting layer 22, and electron injecting layer 23 are thin films made of an organic compound.
In a typical full-color OLED device, there is generally differences in luminous efficiency between respective pixel regions, i.e., the respective colors. For example, a green light emitting material has a higher luminous efficiency than red and blue light emitting materials, and a red light emitting material has a higher luminous efficiency than a blue light emitting material.
As a result, much research has been performed to obtain maximum luminous efficiency and luminance by controlling the thickness of organic thin films. For example, Japanese Published Application No. 4-137485 discloses a technique for improving luminous efficiency by forming the electron transporting layer of a thickness between 30 to 60 nm on a structure that an anode, a hole transporting layer, a light emitting layer, an electron transporting layer, and a cathode are sequentially formed.
Japanese Published Application No. 4-328295 discloses a technique of substantially increasing luminance by controlling the thickness of the electron transporting layer such that the light generated from the light emitting layer interferes with the light reflected from the cathode. Also, Japanese Published Application No. 7-240277 discloses an OLED device that controls an optical film thickness to improve luminance, particularly the color purity of blue light.
The OLED devices described above provide different optical film thicknesses for each color to thereby improve luminance. However, it is very difficult to form optical films of different thicknesses by using different manufacturing processes for each color.